/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javax.servlet;

import java.io.IOException;
import java.util.Enumeration;

/**
 * 
 * Defines a generic, protocol-independent servlet. To write an HTTP servlet for
 * use on the Web, extend {@link javax.servlet.http.HttpServlet} instead.
 * 
 * <p>
 * <code>GenericServlet</code> implements the <code>Servlet</code> and
 * <code>ServletConfig</code> interfaces. <code>GenericServlet</code> may be
 * directly extended by a servlet, although it's more common to extend a
 * protocol-specific subclass such as <code>HttpServlet</code>.
 * 
 * <p>
 * <code>GenericServlet</code> makes writing servlets easier. It provides
 * simple versions of the lifecycle methods <code>init</code> and
 * <code>destroy</code> and of the methods in the <code>ServletConfig</code>
 * interface. <code>GenericServlet</code> also implements the <code>log</code>
 * method, declared in the <code>ServletContext</code> interface.
 * 
 * <p>
 * To write a generic servlet, you need only override the abstract
 * <code>service</code> method.
 * 
 * 
 * @author Various
 * @version $Version$
 * 
 * 
 * 
 */

public abstract class GenericServlet implements Servlet, ServletConfig,
		java.io.Serializable {

	private transient ServletConfig config;

	/**
	 * 
	 * Does nothing. All of the servlet initialization is done by one of the
	 * <code>init</code> methods.
	 * 
	 */

	public GenericServlet() {
	}

	/**
	 * Called by the servlet container to indicate to a servlet that the servlet
	 * is being taken out of service. See {@link Servlet#destroy}.
	 * 
	 * 
	 */

	public void destroy() {
	}

	/**
	 * Returns a <code>String</code> containing the value of the named
	 * initialization parameter, or <code>null</code> if the parameter does
	 * not exist. See {@link ServletConfig#getInitParameter}.
	 * 
	 * <p>
	 * This method is supplied for convenience. It gets the value of the named
	 * parameter from the servlet's <code>ServletConfig</code> object.
	 * 
	 * @param name
	 *            a <code>String</code> specifying the name of the
	 *            initialization parameter
	 * 
	 * @return String a <code>String</code> containing the value of the
	 *         initialization parameter
	 * 
	 */

	public String getInitParameter(String name) {
		return getServletConfig().getInitParameter(name);
	}

	/**
	 * Returns the names of the servlet's initialization parameters as an
	 * <code>Enumeration</code> of <code>String</code> objects, or an empty
	 * <code>Enumeration</code> if the servlet has no initialization
	 * parameters. See {@link ServletConfig#getInitParameterNames}.
	 * 
	 * <p>
	 * This method is supplied for convenience. It gets the parameter names from
	 * the servlet's <code>ServletConfig</code> object.
	 * 
	 * 
	 * @return Enumeration an enumeration of <code>String</code> objects
	 *         containing the names of the servlet's initialization parameters
	 * 
	 */

	public Enumeration getInitParameterNames() {
		return getServletConfig().getInitParameterNames();
	}

	/**
	 * Returns this servlet's {@link ServletConfig} object.
	 * 
	 * @return ServletConfig the <code>ServletConfig</code> object that
	 *         initialized this servlet
	 * 
	 */

	public ServletConfig getServletConfig() {
		return config;
	}

	/**
	 * Returns a reference to the {@link ServletContext} in which this servlet
	 * is running. See {@link ServletConfig#getServletContext}.
	 * 
	 * <p>
	 * This method is supplied for convenience. It gets the context from the
	 * servlet's <code>ServletConfig</code> object.
	 * 
	 * 
	 * @return ServletContext the <code>ServletContext</code> object passed to
	 *         this servlet by the <code>init</code> method
	 * 
	 */

	public ServletContext getServletContext() {
		return getServletConfig().getServletContext();
	}

	/**
	 * Returns information about the servlet, such as author, version, and
	 * copyright. By default, this method returns an empty string. Override this
	 * method to have it return a meaningful value. See {@link
	 * Servlet#getServletInfo}.
	 * 
	 * 
	 * @return String information about this servlet, by default an empty string
	 * 
	 */

	public String getServletInfo() {
		return "";
	}

	/**
	 * 
	 * Called by the servlet container to indicate to a servlet that the servlet
	 * is being placed into service. See {@link Servlet#init}.
	 * 
	 * <p>
	 * This implementation stores the {@link ServletConfig} object it receives
	 * from the servlet container for later use. When overriding this form of
	 * the method, call <code>super.init(config)</code>.
	 * 
	 * @param config
	 *            the <code>ServletConfig</code> object that contains
	 *            configutation information for this servlet
	 * 
	 * @exception ServletException
	 *                if an exception occurs that interrupts the servlet's
	 *                normal operation
	 * 
	 * 
	 * @see UnavailableException
	 * 
	 */

	public void init(ServletConfig config) throws ServletException {
		this.config = config;
		this.init();
	}

	/**
	 * 
	 * A convenience method which can be overridden so that there's no need to
	 * call <code>super.init(config)</code>.
	 * 
	 * <p>
	 * Instead of overriding {@link #init(ServletConfig)}, simply override this
	 * method and it will be called by
	 * <code>GenericServlet.init(ServletConfig config)</code>. The
	 * <code>ServletConfig</code> object can still be retrieved via {@link
	 * #getServletConfig}.
	 * 
	 * @exception ServletException
	 *                if an exception occurs that interrupts the servlet's
	 *                normal operation
	 * 
	 */

	public void init() throws ServletException {

	}

	/**
	 * 
	 * Writes the specified message to a servlet log file, prepended by the
	 * servlet's name. See {@link ServletContext#log(String)}.
	 * 
	 * @param msg
	 *            a <code>String</code> specifying the message to be written
	 *            to the log file
	 * 
	 */

	public void log(String msg) {
		getServletContext().log(getServletName() + ": " + msg);
	}

	/**
	 * Writes an explanatory message and a stack trace for a given
	 * <code>Throwable</code> exception to the servlet log file, prepended by
	 * the servlet's name. See {@link ServletContext#log(String, Throwable)}.
	 * 
	 * 
	 * @param message
	 *            a <code>String</code> that describes the error or exception
	 * 
	 * @param t
	 *            the <code>java.lang.Throwable</code> error or exception
	 * 
	 * 
	 */

	public void log(String message, Throwable t) {
		getServletContext().log(getServletName() + ": " + message, t);
	}

	/**
	 * Called by the servlet container to allow the servlet to respond to a
	 * request. See {@link Servlet#service}.
	 * 
	 * <p>
	 * This method is declared abstract so subclasses, such as
	 * <code>HttpServlet</code>, must override it.
	 * 
	 * 
	 * 
	 * @param req
	 *            the <code>ServletRequest</code> object that contains the
	 *            client's request
	 * 
	 * @param res
	 *            the <code>ServletResponse</code> object that will contain
	 *            the servlet's response
	 * 
	 * @exception ServletException
	 *                if an exception occurs that interferes with the servlet's
	 *                normal operation occurred
	 * 
	 * @exception IOException
	 *                if an input or output exception occurs
	 * 
	 */

	public abstract void service(ServletRequest req, ServletResponse res)
			throws ServletException, IOException;

	/**
	 * Returns the name of this servlet instance. See
	 * {@link ServletConfig#getServletName}.
	 * 
	 * @return the name of this servlet instance
	 * 
	 * 
	 * 
	 */

	public String getServletName() {
		return config.getServletName();
	}
}
